No idea why, but Tracy Tools has Taps and dies:

https://www.tracytools.com/product/1-4-x-24-tpi-w-form/

MichaelG.

My Leinen Lz43 headstock thread is a 55 degree 3.5mm pitch with a 44.5mm diameter..

I hesitate to suggest this, Bill … for fear of triggering  ‘hate’ [*] from the proponents of other thread forms … but, I think the Whitworth thread form was widely adopted because engineers recognised:

1. its technical merits
2. its geometric elegance, and
3. all the effort that went into producing and standardising it

It was, and remains, a fundamentally good design … and Sir Joseph Whitworth was widely respected.

Bottom line … If you wanted a good form for screw-thread; why choose any other ?

It was [as intended] definitive.

MichaelG.

.

[*] an unpleasant word which has now settled in the vocabulary of this group

On 2 January 2024 at 22:11 Bill Phinn Said:

 

 

Why did so many of these non-standard Whitworth threads become established in their own right?

Because we are not just talking about nuts and bolts. For example BSW & BSF are no use for a pipe union. A much finer thread is needed.

I seem to remember reading that metric pipe sizes, and their threading standards, are basically Imperial ones,  but notated (If that’s the right word) in metric units. So a metric 152.3 mm diameter pipe is really the same as a 6 inch pipe. Is this basically correct? I know there are numerous different standards for pipes and tubes of different materials and for different purposes but it does seem as if the Continentals borrowed the British pipe and thread dimensions as fit for purpose but measure the pipes with their own rule. If so, it seems like a tribute to Whitworth and his work.

Whitworth form threads are used in BSW, BSF, BSP, BSB (British Standard Brass) and Model Engineer threads, All of which have their own pitch or pitches. The only ” constant pitch” across all sizes are the BSB at 26 tpi, and the ME threads at 40 tpi and 32 tpi.

There will be other “non standard” pitches, (The early Myford ML1,2,3 and 4, used 7/8 BSW, and then 7/8 x 12 tpi, the “Standard” Myford 1.125 x 12 tpi.  The Warco BH600, BH900, Chester Craftsman, Engineers ToolRoom BL12 -24 all use 2.25 x 8 tpi for the chuck mounting, as no doubt, will other Taiwanese generic lathes.

Posibly Boxford will use a Whit form thread, to distinguish from the South Bend.

Sometimes a “non standard” pitch will be used, deliberately, sometimes to try to maintain a market for spare parts, or finer pitch than the standard for a given diameter, to provode a more precise adjustment.

R P S threads, used in older cameras, lenses and enlargers will be Whit form, but with a finer than standard pitch, plus microscopes.

Howard

As Howard states to maintain a spares supply,  one case in point is the front screws on coventry die heads, the most lost part!!!

On 3 January 2024 at 03:02 Michael Gilligan Said:

… but, I think the Whitworth thread form was widely adopted because engineers recognised:

1. its technical merits
2. its geometric elegance, and
3. all the effort that went into producing and standardising it

It was, and remains, a fundamentally good design … and Sir Joseph Whitworth was widely respected.

Bottom line … If you wanted a good form for screw-thread; why choose any other ?

It was [as intended] definitive.

MichaelG.

 

Not how I read the history.  Whitworth came up with something far cleverer than a mere thread – standardisation.  Given a decent thread, and clear instructions on how to make it, most firms preferred to standardise, not least because they could sack everyone making proprietary threads and buy in cheap mass produced nuts and bolts.  Also made sales easier, because customers dislike being forced to buy proprietary spare parts.

Whitworth form was excellent in it’s day, but two faults gradually emerged:

• Coarse threads are suitable for soft-materials, great when Victorian engineering majored in cast-iron, but not good for steel, or the small diameter nuts and bolts needed for instrument or electrical work.  As these industries developed, it became necessary to think again.
• The rounded form is expensive and fiddly to make, and the extra strength rarely needed. Rounding made good sense when Wrought-Iron bolts went into cast-iron bodies, but unnecessary as materials changed, and for most ordinary purposes.

Rather later in the US, Sellers looked at Whitworth and liked the idea but not the detail.  He decided to simplify, making US industry more productive and cheaper than British industry.  Sellers removed the rounded top and switched from 55° to 60° and this became the US National thread.   Main advantage was standardisation, not geometric elegance!

In the same time-frame, the Europeans standardised on Metric measurement.   In Europe, metric was very much welcomed because it replaced a gazillion local measurements that caused endless trouble with trade.  Europe and the rest of the world also went for 60°.  Metric and US thread forms are very similar, apart from metric being defined in terms of metric pitch, and US being defined in Threads per Inch.

In WW2 the difference between American and British fasteners caused endless trouble, and it was decided to standardise on a Unified System, which is closer to the US National form than Whitworth, thus BSW and BSF started to decline during the 1950s.   UNC and UNF didn’t last long in the UK, because we faced sharp competition from Metric countries, none of whom wanted Inch based fasteners.   By the 1960s the figures showed that most export customers wanted Metric, not Whitworth or UNC/UNF.   Not accepted on many shop-floors and Board Rooms unfortunately, where too many fought tooth and nail to keep the old ways.

My conclusion, ‘the customer is always right’.  And when customers no longer want something, no matter how glorious, the supplier has to move on.

Mistake I suggest to support any technology for sentimental reasons.  Technology is about fixing today’s problems.  Although HMS Victory was arguably the best warship in the world, and has an amazing history of achievement, I hope no-one thinks the ship has any place in a modern Navy.   Likewise, the much more modern USS New Jersey. She too was excellent in her day, but designed for a role that no longer exists, and although not quite obsolete yet, would need major upgrades before she could safely be deployed. Spending big money on technology that’s not needed is always unwise – I see the ship soon becoming a museum piece.

Post Brexit, the government launched a consultation to find out if legislative change was wanted in respect of Imperial and Metric measure.  During the Brexit campaign, there was loud support for Imperial.  The consultation results  are in, full report here.  In summary, the UK emphatically does not wish to undo Metric in favour of Imperial:

Imperial measure served this country well, but clinging to it after 1965 was – in my opinion – a bad mistake. Kept traditionalists happy, but thoroughly confused industry and damaged their ability to sell abroad.

Dave

That’s the great thing about having engineering standards….. there are just so many you can chose from!

And if you don’t like what you’ve got, just invent a few more!

WaaHaaHaa  ha! (carries on banging head against wall).

It’s an age thing, the older the product, the more likely it will be to have weird and wonderful bastard thread sizes and if old Britiron, whitform is the bastard of choice. But save your contempt for the real villains, the ones that insist on using miscellaneous varieties of thread systems on the same item, Myford for example (metric, whitworth as well as whitform and if you are lucky BA!)

A Whit form thread

A thread that would be a Whit thread tap/die size, but without the correct tpi/diameter and still have sufficient strength for the purpose.

eg 4C collets are threaded 20tpi and over 3/4″ in diameter whereas the corresponding proper Whit size dia for 20pti would be 1/4″.

I would expect that a Whit form would conform to the Whit rules of flank angle and rounded tops, which therefore locks in both thread depth and tpi together.

The closely related BSC cycle threads are 60 degrees and not the Whitworth 55 degrees, and BA are an odd metric based thread.